Double piston differential type pump



. Oct. 7, 1969 R. W. ROBIRDS ETAL DOUBLE PISTON DIFFERENTIAL TYPE PUMP Filed May 16, 1967 mvmworzs Mal/7170 14 FOB/Kw; ../0///V F. M/zsa/v, I

Mam, MJHHL 4.11.-

ATTORNEYS United States Patent U.S. Cl. 103-10 9 Claims ABSTRACT OF THE DISCLOSURE A two-piston hydraulic pump which shifts automatically from a two-piston, high volume arrangement while pumping fluid into a low pressure zone to a one-piston, low volume arrangement in response to an increase in load resistance.

BACKGROUND OF THE INVENTION This invention relates to fluid pumps and more particularly to pumps having multiple reciprocating pistons.

The desirability of pumping the maximum volume of hydraulic fluid with the minimum number of strokes of a pump arm actuated by a given force has long been recognized. The volume of fluid displaced by a reciprocating piston type pump is proportional to the surface area of the piston, and the force required to displace the piston is also proportional to the arm of the piston. As the pressure in the pump cylinder increases, the force required to displace the piston also increases. If the force available for pumping is limited, as in a manual pump, for example, and the pressure of the fluid is relatively high, then the volume of fluid that is pumped with each stroke of the piston must be relatively small. However, a pump having a small volume displacement per stroke of the piston is inefficient when used to pump fluids at low pressures.

One prior art approach to the problem of pumping fluids manually at both high and low pressures has been the use of a plurality of pumps. Each pump in the system is designed to operate over a narrow range of pressures, and the appropriate pump is selected by the operator as the load pressure increases. Another approach to this problem has been the use of a compound pump having a plurality of pistons of different diameters. The pistons are connected together by a pump arm with a movable fulcrum for reciprocating one or another of the pistons. The pump operator selects by means of a latch the fulcrum about which the pump arm swings. The pump operator, however, is required to cease pumping in order to operate the latch when the pressure of the fluid resists further displacement of the operating piston.

Accordingly, it is an object to provide a manual pump which operates efficiently over a wide range of pressures.

A further object is to provide a pump which automatically adjusts its operation to displace the maximum volume of fluid possible for a given actuating force.

It is another object of this invention to provide a compound pump having large and small diameter pistons in which the pump arm automatically adjusts for opera tion of either or both pistons in response to the pressure of the fluid being pumped.

SUMMARY OF THE INVENTION The pump of this invention has reciprocating pistons of different diameters. A single pump arm is attached to the rod of each piston for reciprocating the pistons by swinging movement of the pump arm. The cylinders for each piston are connected together by a common passage, with an inlet valve upstream from both cylinders and an outlet valve downstream from both cylinders.

During swinging movement of the pump arm, both pistons reciprocate until the pressure of the fluid in the passage exerts a greater force on the large piston than can be overcome by the operator. The large piston is then locked by the pressure at the top of its stroke and the rod of the large piston serves as the fulcrum for continued pumping with the small piston at a lower volume per stroke, but at a greater pressure.

DESCRIPTION OF THE DRAWINGS The preferred embodiment is illustrated in the accompanying drawings, in which:

FIG. 1 is a longitudinal cross-sectional view of the P p;

FIG. 2 is a cross-sectional view of the pump along the line 2-2 in FIG. 1; and

FIG. 3 is an end view of the pump.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, the pump body or housing 10 is bored so as to provide an elongated fluid chamber 12 therein. This elongated fluid chamber is provided at one end with a fluid inlet port 14 and a fluid outlet port 16 and is sealed at the other end by a threaded plug 17. Located 'between the fluid chamber 12 and the ports 14 and 16 are ball sealing check valves 18 and 20. The housing 10 is mounted upright on a suitable support, so that balls in the check valves 18 and 20 are urged against their respective valve seats by gravity.

In the housing 10 and in fluid communication with elongated fluid chamber 12 intermediate the ends thereof is a low pressure cylinder 22. A high pressure cylinder 24 is provided in the housing 10 on the opposite side of the cylinder 22 from the valves 18 and 20. The central axes of the cylinders 22 and 24 are substantially parallel to each other. Mounted for reciprocating movement within the cylinder 22 is a piston 26 having a piston rod 28 which extends upwardly through a seal 30 and a seal retaining cylinder cap 32. Formed integrally with the piston rod 28 of the piston 26 is piston rod extension 34. The cylinder 22 is sealed at its lower end by a threaded plug 36. An apertured spacer 38 is secured to the plug 36 and serves to arrest the downward motion of piston 26 short of completely obstructing the flow of fluid along the length of fluid chamber 12. The spacer 38 has a plurality of openings 39 which allow fluid to flow through the hollow interior of the spacer.

Similarly mounted within the high pressure cylnider 24 is a piston 40 having a reduced diameter piston rod 42 formed integral therewith. The piston rod 42 extends upwardly through the fluid chamber 12, seal 43 and threaded cylinder cap 44. The lower end of cylinder 24 is threaded so as to receive a plug 45 axially bored to provide an air vent 47.

A rigid pump arm 46 is provided to reciprocate the pistons 26 and 40 within their respective cylinders. One end of the arm 46 has a handle 56 and the other end is pivotally attached to the piston rod 42 by means of linkage 48 and pins 50 and 52. The piston rod extension 34 is pivotally attached by a pin 54 to the pump arm 46 at a point spaced from the end of the arm.

The piston rod 42 is subjected to a lateral stress during reciprocating movement of the piston 40. This stress is caused by the arcuate movement of the end of the pump arm 46, although the linkage 48 reduces the lateral stress considerably. By pumping with the rod end of the piston 40, rather than the head end, the supported length of the piston 40 and the piston rod 42 is considerably increased over an arrangement wherein the head end of the piston is used for pumping. The rod seal 43 and a piston seal 51 guide the rod and piston respectively on opposite sides of the chamber 12. Secondly, during the pressure stroke of the piston 40 the force is applied through the linkage 48 to the rod 42 by pulling rather than by pushing the piston rod 42.

The upper end of each cylinder 22 and 24 has a shoulder 58 and 60, respectively that is in position to be engaged by the rod ends 62 and 64 of the respective pistons. The shoulders 58 and 60 limit the stroke of the pistons upwardly in the housing 10. The downward stroke of the large piston 26 is limited by the spacer 38, while the stroke of the small piston is restricted by the plug 45. The chamber 12 communicates with the cylinder 24 at the rod end of the piston 40, while the chamber 12 communicates with the cylinder 22 at the head end of the large piston 26. By this arrangement, a relatively large piston rod 42 connects the piston 40 with the arm 46. but the ratio of the cross sectional areas of the two pistons that are exposed to fluid in the chamber 12 is also large. Thus, mechanical strength is provided without sacrificing the efliciency of operation. Preferably, the ratio of cross sectional areas of the pistons 26 and 40 is about to 1.

In operation against a low fluid pressure at the outlet port 16, the pressure of the fluid is applied through the outlet port 16 to the balls of check valve 20 to maintain the balls against their seats. The halls of the inlet check valve 18 are also lodged on the seats, initially. The pump elements initially are in the position shown in FIG. 1. Upward movement of the pump arm handle 56 causes rotation of the pump arm 46 about the pin 52, which serves as a fulcrum. Downward movement of the piston 40 is restricted by the plug 45, while the large piston 26 is drawn upwardly by the arm 46. As the piston 26 moves upwardly, fluid flows into the chamber 12 through the oneway valve 18. Continued upward movement of the handle 56 is arrested by abutment of the rod end 62 with the shoulder 52 in the large cylinder 22.

As the handle 56 of the pump arm 46 is moved downwardly, the fulcrum upon which the pump arm 46 rotates is shifted to the pin 54, since the piston 26 has a larger cross sectional area than the rod end of the piston 40. Rotation of pump arm 46 causes the small piston 40 to rise and to displace fluid from within the cylinder 24 through the check valve 20 and out of the housing through the outlet port 16.

When the upward movement of the piston 40 is arrested by abutment of the rod end 64 with the shoulder 60, the downward movement of the handle 56 continues, but the fulcrum shifts from the pin 54 to the pin 52. R0- tation of pump arm 46 then forces the piston 26 downward while displacing the fluid from the cylinder 22, through the check valve 20 and out of the housing through the outlet port 16. The discharge stroke is completed when the downward movement of piston 26 is arrested by abutment with spacer 38.

The suction stroke is commenced again by the upward movement of the handle 56. The small piston 40 is forced downward as the pump arm 46 rotates about the pin 54. At the same time, the piston 26 begins to move upwardly in the cylinder 22. This causes fluid to be drawn into the chamber 12, through the check valve 18. Both pistons are thus utilized for pumping as the cycle is repeated.

As the fluid pressure at the outlet port 16 increases, it becomes increasingly difficult to apply enough manual force to the handle 56 to move the piston 26 against the pressure in the fluid chamber 12. Consequently, the piston 26 has become hydraulically locked by engagement of the rod end 62 with the shoulder 58 at the top of cylinder 22, and the fulcrum upon which the pump arm 46 rotates is fixed at the pin 54. Continued oscillation of the handle 56 then causes the piston 40 to reciprocate. The net cross sectional area of the rod end of the piston 40 exerts a resisting force on the rod 42 that is much smaller than that of the large piston 26 at the same pressure in the chamber 12, because of the difference in exposed areas of the pistons. Since the manual force applied to the handle is greater thatn the resisting force on the piston 40, the pump can continue to operate, but at a reduced volume. The are through which the handle 56 swings in the high pressure, single piston operation of the pump is shorter than the arc described in the low pressure, two piston operation.

The pump of this invention provides efficient manual pumping of fluid, with a minimum number of strokes of the pump arm. When installed in a system where the outlet pressure rises as fluid is pumped out of the chamber 12 through the valve 16, a large volume of fluid is pumped initially by both pistons during each up and down cycle of the pump handle 56. When the pressure in the chamber 12 is sufliciently high to lock the piston 26 at the top of the cylinder 22, pumping continues with the small piston only. The shift in operation is accomplished without requiring any adjustment of the pump by the operator. The arrangement of the pump cylinders provides a pump that is serviceable for a long period of time without requiring repair or replacement of seals or piston rods due to wear.

What is claimed is:

1. A pump comprising:

a housing having a first cylinder and a second cylinder formed therein,

a fluid chamber in said housing in fluid communication with said first and second cylinders,

a first piston mounted for reciprocating movement within said first cylinder, a second piston mounted for reciprocating movement within said second cylinder, said second piston having a smaller cross-sectional area than said first piston,

means for limiting the length of reciprocating movement of said first and second pistons,

an elongated pump arm, means for pivotally connecting said first piston to said pump arm for pumping movement in a first direction relative to said fluid chamber, means for pivotally connecting said second piston to said pump arm for pumping movement in a second direction relative to said fluid chamber, said second direction being generally opposite to said first direction, said first and second piston connecting means being spaced apart along the length of said pump arm,

inlet valve means communicating with said chamber,

including means for restricting fluid flow to unidirectional flow into said chamber, outlet valve means communicating with said chamber, including means for restricting fluid flow to unidirectional flow out of said chamber,

whereby oscillating movement of said pump arm reciprocates said first and second pistons when the fluid pressure in said chamber is low and reciprocates said second piston when the fluid pressure in said chamber is sufliciently high to resist movement of said first piston by said pump arm.

2. A pump in accordance with claim 1 wherein said fluid chamber is elongated and said first and second pistons reciprocate along parallel axes which are spaced apart longitudinally of said chamber.

3. A pump in accordance with claim 1 wherein said fluid chamber is elongated, said inlet and said outlet valve means are adjacent one end of said elongated fluid chamber and said first and second cylinders are spaced longitudinally of said chamber from said valve means.

4. A pump comprising:

a housing having a first cylinder and a second cyinder formed therein,

a fluid chamber in said housing in fluid communication with said first and second cylinders,

a first piston mounted for reciprocating movement within said first cylinder, a second piston mounted for reciprocating movement within said second cylinder, said second piston having a smaller crosssectional area than said first piston,

means for limiting the length of reciprocating movement of said first and second pistons,

an elongated pump arm, means for pivotally connecting said first piston to said pump arm, means for pivotally connecting said second piston to said pump arm, said first and second piston connecting means being spaced apart along the length of said pump arm,

inlet valve means communicating with said chamber,

including means for restricting fluid flow to unidirectional flow into said chamber, outlet valve means communicating with said chamber, including means for restricting fluid flow to unidirectional flow out of said chamber,

whereby oscillating movement of said pump arm reciprocates said first and second pistons when the fluid pressure in said chamber is low and reciprocates said second piston when the fluid pressure in said chamber is sufficiently high to resist movement of said first piston by said pump arm,

said fluid chamber being elongated, and a portion of said fluid chamber between said first cylinder and said second cylinder being unobstructed by valves,

said inlet and outlet valve means being adjacent one end of said elongated fluid chamber, and said first and second cylinders being spaced longitudinally of said chamber from said valve means,

said second cylinder being adjacent the other end of said chamber, said first cylinder being positioned between said valve means and said second cylinder, said first piston being movable into and out of said chamber, said piston movement limiting means including a spacer in said chamber in position to be engaged by said first piston, said spacer having a passage therethrough, whereby said spacer maintains fluid flow through said chamber when said first piston has moved into said chamber.

5. A claim in accordance with claim 4 including a plug in said housing adjacent said first cylinder, said spacer being secured on said plug.

6. A pump comprising:

a housing having a first cylinder and a second cylinder formed therein, said cylinders each having a central axis and said central axes being substantially parallel,

a first piston mounted for reciprocating movement in said first cylinder, a second piston mounted for reciprocating movement in said second cylinder,

a first piston rod secured to the rod end of said first piston, a second piston rod secured to the rod end of said second piston, said piston rods extending outwardly through said housing on one said thereof,

an elongated pump arm, means for hingedly connecting said second piston rod to one end of said arm, means for hingedly connecting the said first piston rod to said arm at a point spaced from said one end,

said housing having a fluid chamber and inlet and outlet ports therein, inlet valve means providing unidirectional flow into said chamber from said inlet port, outlet valve means providing unidirectional flow out of said chamber through said outlet port, said chamber extending between said inlet and outlet valve means and said cylinders and being continously in fluid communication with said second piston rod end and with the end of said first piston opposite said rod end,

said second piston having a smaller exposed cross sectional area at said rod end than said first piston at said opposite end,

whereby the pumping stroke of said second piston occurs during outward movement of said second piston rod.

7. The pump according to claim 6 including shoulder means in said housing for limiting movement of said piston rods outwardly of said housing, whereby said sec ond piston engages said shoulder means while said first piston is displaced away from said shoulder means by said handle.

8. The pump according to claim 6 including rod packing means in said housing in engagement with said second piston rod, and piston packing means in said housing in engagement with said second piston, whereby said packing guides said second rod and piston during reciprocating movement by said arm.

9. The pump according to claim 7 wherein said second piston rod connecting means includes a rigid linkage between said piston rod and said arm, and pins connecting said linkage to said rod and said arm, whereby said linkage compensates for arcuate movement of said arm end.

References Cited UNITED STATES PATENTS 2,337,831 12/1943 McGovern -52 2,341,318 2/ 1944 Forbes. 2,372,375 3/1945 Groves 10337 2,414,484 1/ 1947 Page 60-52 2,472,104 6/ 1949 Grant et al. 103-38 3,112,705 12/ 1963 Chlebowski 60-52 WILLIAM L. FREEH, Primary Examiner U.S. Cl. X.R. 10337 

